the need to insert the blade bowed so that it mostly straightens as the frame itself bows under tension (which may be visible in the photo of my fret saw).
This is another good point. The back of my less expensive saws is not as rigid as the back of the KC saw. It may be the non-rigid tendency of the backs or the difficulty of getting as high of tension on my one saw that causes me to break blades.
My smaller saw is preferred over the two German saws since it is lighter and less clumsy to use. It doesn't have the blade tensioning screw like the German saws.
jtk
"A pessimist sees the difficulty in every opportunity; an optimist sees the opportunity in every difficulty."
- Sir Winston Churchill (1874-1965)